Manufacture of monoalkali-metal phosphate.



ATE F EMEEsoN H. STRICKLER, OF NEW YORK, N. Y., AssIe oE' T0 GENERALCHEMICAL",

COMPANY, on NEW YORK, N. Y., A CORPORATION OF NEW YORK.

MAN'tTFACTURE OF MONOALKALI-ME'IAL PHOSPHATE.

No Drawing.

To all whom it may concern Be it known that I, EMERSON H. STRIQK- LER, a.citizenjof the United States, and a resident of the city of New York,State of' New York, have invented certain new and useful Im rovements inthe Manufacture of Monoalka i-Metal Phosphate, of which the following isa. specification.

My invention relates to the manufacture of mono-alkali metal phosphates,an example of which is mono-sodium phosphate which is stated to have,apart from water of crystallization, the formula NaH,PO'

An object of my'invention is to provide a novel process for theproduction of monoalkali metal phosphates by which a substantially pureproduct. is capable of being obtained on a commercial scale and at acommercially reasonable cosh;

Another object is to provide a cyclic process for the production ofmono-alkali metal phosphate in which the residue, after the mono-alkalimetal phosphate has been separated out, is introduced into an earlierstage of the complete process, such as that stage at whichtri-alkali-metal phosphate is made for example in accordance with ther-ocess set forth in my Letters Patent No. 744,128, dated November 17,1903, or in my Letters Patent No. 1,037,837, dated September 3,1912. yOther objects will be pointed out or will otherwise appear in thefollowing description of my invention, in which, as well as in theappended claims, I use the term alkali metal phosphate to include thediand tri-alkali-metallic salts of phosphoric acid,

such as .or potassium; di-alkali metal phosphate to includedi-sodiumphosphate and di-potassium phosphate; trialkalimetal phosphate toinclude tri-sodium phosphate and tri-potassium phosphate; mono-alkalimetal phosphate to nclude mono-sodium phosphate and monopotassiumhosphate; and acid to include 1 acids free om phosphorus, such assulfuric,

nitric and hydrochlorieacids.

Heretofore. IIlOIlO-SOdllJIIl phosphate has been a laboratory productonly. The laboratory methods of producing it are (1) treating phosphoricacid (H P carbonate until the mixture is neutral, using methyl orange asan indicator; '(2) treating phosphate or di-sodium phos- Speeifieatio'nof Il'etters Patent.-

, with sodium phate with phosphoric acid; or, (3) adding alcohol to asolution of di-sodium phosphate in nitric acid.

For commercial and technical purposes,

commercial and technical operations and,

which contaminate the mono-sodium phosphate produced therefrom inaccordance with the first two of the above methods, and,

in the 'case of thethird laboratory method,-

owing to the prohibitive cost of, the alcohol. On the other hand' myimproved process of making mono-alkali metal phosphates, which, ofcourse, includes mono-sodium phosphate, is both a commercially availableprocess and'one which results in a product commercially free from1ron,'alumma, and

Patented Aug. 24., 1915.

Application filed March 23, 1912. Serial No. ceases.

the other impurities above mentioned, a

product which is only accompanied by small and for practical purposes,negligible amounts of other alkali metal salts, such as, for example,sodium sulfate, sodium I chlorid, sodium nitrate. By proper methods ofpurification,.-such as crystallization, the

amounts of such accompanying salts can be reduced to any desired degree.

Broadly stated my invention consists in treating an alkali metalphosphate with an .acid free from phosphorus, such as sulfuric acid,hydrochloric acid,- or nitric .acid, in such a manner as to liberate allthe phosphoric acid contained in the alkali metal phosphate, separatingthe phosphoric acid from the salt of the acid which has been used'andtreating the phosphoric'acid with a further amount of alkali metalphosphate in such a manner as to produce mono-alkali metal phosphate.The liquor containing phosphoric acid and thesalt of the added acid ispreferably treated to separate its constituentsby removing the .salt ofthe added acid. It is obvious that the removal of the salt-of the addedacid maybe effected subsequently to the final addition of alkali metalphosphate, but this method is found not to be so-eflicient' as the firstmentioned process.

.When" the phosphoric acid is separated ess of making mono-alkali metalphosphate.

There is thus evolved a cyclic process in which all of thealkali metalproducts of phosphoric acid are utilized. The mono-- alkali metalphosphate, moreover, is produced in a substantially pure condition. In

this cyclic process, a complete separation of the phosphoric acid andthe salt of the added acid is obviously unnecessary because in any caseall of the phosphorus contained' in the original phosphate is utilized.

In the practice. of that example of my cyclic process in which I employsulfuric acid as the added acid and which includes the process set forthin the above Patent 744,128, tri-sodium phosphate is made by treating.rock phosphate 5. 6. calcium phosphate with a solution of niter cake andfurnacing the solution thus obtained in the presence of a carbonaceousmaterial, thetrisodium phosphate thus made is then treated with sulfuricacid in such a manner as to produce phosphoric acid 'andrsodium sulfate,the last mentiond constituents are then separated and the sodium sul:

1 fate, carrying with it small amounts of phosphate, is then utilized;as ,above set forth, 1n the manufacture of more tri-sodi- 'um phosphate.The phosphoric acid is treated with a further amount of tri-sodiumphosphate to produce mono-sodium phos-' phate. I have-described mycyclic process in which sulfuric acid is used and the sulfate of sodaproduced-is employed in the preparationof the tri-sodium phosphate. Itwill be understood, however, that the salts of the other added acids mayby suitable modifications be employed with equally successful results.If another acid than sulfuric has beenused, the salt of the added acidmay obviously be converted into a sulfate by treatment with sulfuricacid so that the processes hereinbefore referred tomay be utilized forproducing tri-alkali metal phosphate. To the sodium sulfate, produced orrecovered whatever way, the proper amount of crude phosphoric acidshould be added so that the proportion between the sulfur and thephosphorus in the resulting mix is that prescribed in my abovereferred'to patent.

Various methods may be used to separate the constituents of the liquorroduced by the treatment of alkali metal p osphate;

with acid. Furthermore, the processes of my invention are susceptible ofvarious slight changes in detail.

To illustrate the nature of my invention the following examples aregiven. These examples are to be considered as illustrative only.

OPERATING WITH DI-S ODIUM PHOSPHATE.

Crystallized di-scdium' phosphate, contains approximately 12 molecularproportions of water of crystallizatlon; z'. 6. ap-' proximately 60% ofwater. In carrying out my new process with this product I have found itadvantageous to take into account the solvent action of the water sointroduced into the process and in the case of an acid containing muchwater such as strong hydrochloric acid, weak sulfuric acid or aweaknitric acid to use even practically dehydrated di-sodium phosphate.

Tri-sodium phosphate may stead-of di-sodium phosphatein all of theprocesses described for the latter, the proc-' esses and results beingsubstantially the same. A. Using sulfuric acid as the added acid.

Example 1.

' Add sulfuric acid, preferably in the'form of a 98% acid to sodiumphosphatecrystals or solution (crystals preferred) until the mixture isneutral to methyl orange; then add a further quantity of sulfuric acidequal to that? required for neutralization; boil.

be used 'indown until a sample of the solution when filtered fromthe.undissolved material yields a filtrate which tests 60 Be and remove thesolidby filtering or otherwise.

To the filtrate add di-sodium phosphate until it tests neutral tomethyl-orange;

.then concentrate-to 50 Be and proceed to separate the mono-sodiumphosphate bv cooling and crystallizing.

B. Using hydrochlil'rcz'z as the added Y Example 2.- Neutralizedi-sodium phosphate with hydrochloric acid using methyl orange asindicator. Then add a further quantity of hydrochloric acid equal inamount to that first added; concentrate the mixture by evaporation untila sample portion of the mixture yields a filtrate which tests 5860 B.Then separate the undissolved material by filtratlon or otherwlse. It spreferable to allow the mixture to cool before making-the separation.The separated salt 'is principally sodium chlorid.

filtrate add 'di-sodlum phosphate To, the v until it is neutral tomethyl orange; allow to cool and crystallize. The crystals thus obtainedare mono-sodium phosphate.

I Concentrate the mother liquor by evaporation and again crystallize.The crystals C. Using nitric acid as the added acid;

Ewampie 3.

Neutralize di-sodium phosphate with nitric acid, using methyl orange asan 1nd1- cator. Concentrate by evaporation until the mixture, with itssuspended solids,tests 64 -B'; addan amount of concentrated nitric acidequal to that required for neutralization; cool and separate byfiltering or other;- wise. The separated material is largely if notwholly sodium nitrate. Concentrate the filtrate to 60 B' by boiling; adddisodium phosphate until the solution is neutral to methyl orange;concentrate to 55? B The crysand allow to cool and crystallize. tals aremono-sodium phosphate.

The mother liquor may be, concentrated and crystallized. The final"liquors including the sodium nitrate crystals separated above are usedfor making sodium phosphate.

The several grades of mono-sodium phosphate obtained in all theforegoing examples are, if necessary, further purified by suitablecrystallization; applying the ordinary experience .andrules obtaining insuch practice, the mono-sodium phosphate can be freed from accompanyingsalts of the added acids to any extent needful in commercial operation.In the preceding examples, furthermore, trisodiumphosphate may be usedin-' stead of di-sodium phosphate, with correspondingly similar results,the proportions of theadded materials, of course, being difacid andtreating the phosphoric acid with suflicient alkali metal phosphate toproduce mono-alkali metal phosphate, substantially as described.

2. The process of making mono-alkali metal phosphate which consists intreating alkali metal'phosphate with sufficient acid to produce freephosphoric acid and an alkali metal salt of the added acid, suitablyconcentrating this product to precipitate the salt of the addedacid,removing the precipitated salt from the phosphoric acid, and treating. jI

the phosphoric acid withsuflicient' alkali metal phosphate to producemono-alkali metal phosphate, substantially as described.

3. The cyclic process of making monoalkali metal phosphate whichconsists in treating alkali metal phosphate with sufiicient acid toproduce free phosphoric acid and an alkali metal salt of the added acid,separating the last-mentioned salt and the phosphoric acid, treating thephosphoric acid with sufiicient alkali metal phosphate to producemono-alkali metal phosphate, converting the separated salt of the addedacid into alkali metal phosphate and utilizingthe last mentioned alkalimetal phosphate in a repetition of the above operations, substantiallyas described. v

4. The cyclic process of making monoalkali' 'metal phosphate whichconsists in first making trialkali "metal phosphate by treating -aphosphate containing substance with an acid alkali metal sulfate andfurnacing the result in the presence of a car-' bonaceous material, thentreating the trialkali metal phosphate, thus produced with an acid. freefrom phosphorus to produce free phosphoric acid and an alkali metal saltof the added acid, then separating the last mentioned salt andthephosphoric acid,

then. treating the phosphoric acid with sufli-s cient alkali metalphosphate to produce mono-alkali metal phosphate and then converting theseparated salt of the added acid into acid alkali metal sulfate andutilizing the last mentioned acid alkali metal sulfate in a-repetitionof the above operations, substantially as described.

t )5. The cyclic process of making'monosodium phosphate which consistsin first making tri-sodium phosphate by treating a duced with sufficientsulfuric acid to produce free phosphoric acid and sodium sulfate, thenseparating the sodium sulfate and the phosphoric acid, then treatlng thephosphoric acid with suflicient sodlum phosphate to producem'ono-sodiumphosphateand thenconverting the sodium sulfate into ,acidsodium sulfate and utilizing the last mentioned acid sodium sulfate in arepeti- 1 tion of the above operations, substantially as described.

In testimony whereof, I have hereunto set my hand in the. presence oftwo. subscribing witnesses. v v

' EMERSON-H. STRICKLER. Witnesses: a)

HoMnRW. HILL'IER BERNHAR'D C. Hnssn.

